1. Field of the Invention
This invention relates to an ultrasonic diagnostic apparatus for producing an image, for example, a sectional image, of an examined body by emitting a beam of ultrasonic wave thereinto and receiving related echoes therefrom.
2. Description of the Prior Art
Typical ultrasonic diagnostic apparatuses emit a beam of ultrasonic wave into an examined body, and receive related ultrasonic echoes therefrom. The received ultrasonic echoes are converted into corresponding electric echo signals. A sectional image of the examined body is generated in response to the electric echo signals.
To increase the S/N (signal-to-noise) ratio of the image of the examined body, a filter tuned to the frequency bands of the electric echo signals is provided which removes noise components from the electric echo signals. Generally, the frequency band of an electric echo signal moves toward a lower side as the electric echo signal relates to a deeper portion of an examined body. Thus, the filter is generally of the tunable type, being responsive to a tuning control signal. The pass band of the filter is adjusted in response to the tuning control signal so as to match the frequency band of a currently-processed electric echo signal.
The control-signal response characteristic and the frequency response characteristic tend to vary from filter to filter. Accordingly, in each ultrasonic diagnostic apparatus, complicated adjustment containing manual processes is usually required to compensate for such a characteristic variation regarding a filter.